Turbine vanes, such as turbine stator vanes or rotor vanes, the latter being also known as turbine blades, are subjected during operation in a gas or steam turbine to hot gas or steam. Thus, they need an active cooling, which is achieved by passing a cooling fluid such as air through internal passages of the vanes known as cooling channels.
The pressure drop and flow-rate of the cooling fluid is determined inter alia by the internal geometry of each vane and in particular of its cooling channels, and may vary depending on manufacturing tolerances affecting for example the cross-sectional areas of the cooling channels. Further, the same type of vane may be used in different types or versions of turbines, and further in different fields of operation, which may result in different firing temperatures and/or different life requirements. Thus, varying demands regarding the flow of the cooling fluid may exist.
In view of these varying requirements, the vanes are typically manufactured to match the highest cooling demands and/or worse-case manufacturing tolerances related to a desired cooling flow. For example, cross-sectional areas of the cooling channels are determined to be sufficiently large for guaranteeing a sufficient flow of cooling fluid even under the hottest firing temperatures to be expected. This, however, results in a loss of performance, since on the one hand cooling fluid and in particular cooling air mixes, when leaving the turbine vane, to the hot gas in the turbine and thus reduces its energy level. On the other hand, cooling air is drawn from the compressor, thereby reducing pressure and energy of the compressed air.
Accordingly, there is a need for providing turbine stator and/or rotor vanes having a better efficiency, improving the performance and power output of different types of turbines under varying, pre-specified conditions, while on the other hand meeting given life requirements.